Network Redundancy via Out-of-Band and In-Band Control Channels
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Solution Overview
Problem
In network systems using the OpenFlow technique, the separation of switch and control server for packet forwarding and route information determination leads to limitations in availability and expandability due to the need for dedicated lines, and potential disruptions if the control channel is disconnected.
Innovation Solution
Implementing a redundancy mechanism by connecting switches to both out-of-band and in-band control servers via separate control channels, allowing the out-of-band control server to register flow entries for control messages to be forwarded to the in-band control server, ensuring continuous communication and redundancy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a dedicated control channel is used to connect switch and control server, then communication reliability is improved, but device complexity and availability are worsened due to requirement for dedicated ports and links
Solution Approach 1:
The control channel is segmented into two independent paths: out-of-band control channel for primary control communication and in-band control channel for backup control communication. This segmentation allows the system to use existing network infrastructure for one path while maintaining dedicated connectivity for the other, resolving the contradiction between reliability and complexity.
Solution Approach 2:
The in-band control server acts as an intermediary backup control server that provides redundant control channel functionality. When the primary out-of-band control server is unavailable, the in-band control server mediates control communication, ensuring continuous operation without requiring dedicated hardware resources.
2Stability of the object's composition
If dedicated control channel is used, then control communication stability is improved, but network availability is worsened when control channel is disconnected
Solution Approach 1:
The in-band control channel is established in advance as a backup cushion against potential failures of the out-of-band control channel. Flow entries are pre-configured to redirect control messages to the in-band control server when the primary control channel fails, ensuring continuous availability without sudden disruption.
Solution Approach 2:
The system dynamically changes the control channel parameter (switching between out-of-band and in-band paths) based on the operational status of the primary control channel. When disconnection is detected, the system transitions to alternative control communication parameters, maintaining stability and availability.
3Device complexity
If only out-of-band control server is used, then device complexity is reduced, but adaptability is worsened due to inability to handle control channel failures
Solution Approach 1:
The in-band control server provides multi-functionality by serving as both a backup control server and a load sharing option. The control system can universally use either out-of-band or in-band control channels depending on availability and configuration, enhancing adaptability without significantly increasing complexity.
Solution Approach 2:
The control server configuration is made dynamic by allowing switches to dynamically select between out-of-band and in-band control channels based on real-time operational conditions. This dynamic adaptability enables the system to handle control channel failures gracefully while maintaining relatively simple configuration.
4Reliability
If redundancy mechanism is implemented with both out-of-band and in-band control servers, then network reliability is improved, but device complexity increases
Solution Approach 1:
The in-band control channel creates a functional copy of the out-of-band control channel's redundancy role. Instead of duplicating all control infrastructure, the system copies the redundancy function using existing network resources, achieving reliability improvement with manageable complexity increase.
Data Source
AI summary
In a network system in which a switch forwarding packets and a control server determining route information are separated, it is desired to achieve a redundancy of the control channel by an out-of-band control channel and an in-band control channel, when the switch receives a control message regarding the flow entry registration and the like based on the route information from the control server. Specifically, the separated switch and control server are connected by a control channel for sending and receiving the control message. The switch is not only connected to a control server via an out-of-band control channel by a route dedicated to the control message, but also connected to another control server via an in-band control channel by a route which is common with a normal data communication for determining the route information, to achieve a redundancy of the control channel.